Increased vascular permeability contributes to a variety of ailments, including vision threatening retinopathies, such as diabetic retinopathy, macular edema, uveitis, and ischemic retinopathies. Changes in the permeability of the vascular bed in the central nervous system also contribute to the pathology of brain tumors and stroke. Vascular permeability is regulated, at least in part, by tight junctions, seams between cell membranes that form a barrier against passage of materials between cells. Post-translational modification of tight junction proteins, e.g., protein phosphorylation, plays a role in disease progression. For example, diabetes increases expression of vascular endothelial growth factor (VEGF), which alters vascular permeability. VEGF-induced permeability requires the phosphorylation, ubiquitination, and internalization of the tight junction protein occludin in a classical protein kinase C (PKC)-dependent manner.
PKC designates a class of kinases which play central roles in key cell signaling processes such as gene expression and regulation of cell growth. There are numerous isoforms of PKC typically classified as: 1) “calcium-dependent” conventional isoforms (“cPKC”) which are regulated by both calcium and diacylglycerol (DAG), such as PKC-beta; 2) “calcium-independent” novel isoforms (“nPKC”) which are regulated by DAG but do not require calcium, such as PKC-delta; and 3) “atypical” isoforms (“aPKC”) which do not require calcium for activation and which are not regulated by DAG. Atypical PKC isoforms include PKC-zeta and PKC-iota (human) (also called PKC-lambda in mice), and generally consist of five functional domains: a Phox/Bem1 (PB1) domain at the N-terminus, an auto-inhibitory pseudosubstrate domain having 12 amino acids, a modified zinc finger-like C1 domain, an ATP binding domain, and a kinase domain at the C-terminus. The PB1 domain interacts with a variety of other proteins (e.g., partition defective homologue (PAR)-6 and mitogen-activated protein kinase kinase (MEK)) through an octicosapeptide repeat (OPR), Phox and CDC (PC) domain, or the aPKC-interacting domain, collectively termed the OPCA motif (Diaz-Meco et al., Mol. Cell. Biol., 21:1218-1227 (2005); Ponting et al., Trends Biochem. Sci., 27:10 (2002); and Berra et al., EMBO J., 14:6157-6163 (1995))). The pseudosubstrate domain is similar to a PKC phosphorylation site but with an Ala substituted for a Ser which inhibits kinase activity until activation induces a conformational change displacing the auto-inhibitory region. Atypical PKCs function independently of DAG but retain a modified C1 domain containing a cluster of basic residues not seen in cPKCs. Additionally, two residues at the C-terminus, Thr410 for PKC-zeta (Thr412 for PKC-iota) and Thr560 for PKC-zeta (Thr555 for PKC-iota) are phosphorylation sites required for activity (Steinberg et al., Physiol. Rev., 88:1341-1378 (2008)).
Atypical PKC represents a target for interfering with the cascade of events leading to vascular permeability induced by growth factors such as VEGF and inflammatory cytokines. The invention provides compounds, compositions, and methods for inhibiting or reducing vascular permeability and regulating aPKC activity.